The present disclosure relates generally to optical waveguide fabrication and, more particularly, to a method and apparatus for forming tapered waveguide structures.
Communication systems continue to be developed in which optical waveguides such as optical fibers are used as conductors for modulated light waves to transmit information. These fibers may be utilized for long distance communication networks, fiber-to-home networks, wide area networks, and/or local area networks. Moreover, with recent advances in information processing technology involving computers and the like, the need and desire to process and transmit massive amounts of data at high speeds have increased. As such, optical components have continued to become more and more reduced in size as the degree of integration thereof is increased.
In certain optical applications, the out-of-plane coupling of light from light emitting devices such as laser diodes (e.g., a Vertical Cavity Surface Emitting Laser or “VCSEL”) through light carrying structures (e.g., an optical fiber or other waveguide structure) requires ultra-precise waveguide geometries in the fabrication of such components. For example, FIGS. 1(a) and 1(b) illustrate an exemplary optical coupling system 100 in which a VCSEL 102 emits a vertically oriented light beam 104 to be propagated through a waveguide 106 along a horizontal path with respect to the vertical axis of the light beam 104. The waveguide 106 (shown as a multimode waveguide in FIG. 1(a), and as a single mode waveguide in FIG. 1(b)) further includes a downwardly tapered surface 108 that essentially acts a 45 degree mirror to reflect the upwardly directed incident optical beam 90 degrees horizontally down the waveguide 106.
In order to maintain efficient optical coupling within the system 100, the alignment tolerances of the components are generally required to fall within precise ranges. For example, the angle of the waveguide taper itself (e.g., a 45 degree angle) should be accurate to within about +/−2 degrees. In addition, the actual location of the taper with respect to the waveguide itself should also be accurate to within about 0.5 μm. Thus, it will be appreciated that in order to produce a practical tapered waveguide coupling system, a cost-effective manufacturing process is desirable.
In the past, several methods have been implemented to produce these tapered waveguide structures. One example of an existing method of tapered waveguide formation involves the use of a gray scale mask to define the desired waveguide pattern and thereafter performing reactive ion etching to transfer the pattern directly into a waveguide layer material formed on a substrate. Although this method has shown promising results, it is extremely process intensive. In addition, the accuracy of the transferred taper angle is highly sensitive to the process variables such as type of photoresist, etch conditions, etc. As a result, the goal of achieving a reliable, repeatable process using a grey scale mask and/or other direct etching techniques may be a difficult proposition.